Objective To examine the effects of nitric oxide on LHRH release in vitro. ABSTRACT:L-arg, the substrate required for nitric oxide synthesis, or D-arginine (D-arg), the inactive form of the molecule, at 1 nM were perifused into tissues from the medio-basal hypothalamus and medial preoptic area of adult monkeys using a perifusion system. L-arg induced a significant increase (p<0.01, n=12) in LHRH release from both medio-basal hypothalamus and medial preoptic area tissues, while D-arg failed to induce a stimulation (n=8). The results suggest that L-arg does stimulate LHRH release and nitric oxide may be important for the pulsatility of LHRH release in the non-human primate. Keywords Nitric oxide, LHRH release, L-arginine, D-arginine